The present invention generally relates to sensors and, more particularly, to a method of compensating bias drift for sensors, such as angular rate sensors.
Automotive vehicles are increasingly employing various sensors including angular rate sensors for use in vehicle stability control and rollover detection. These sensors are generally employed to sense a condition and produce an output signal indicative of the sensed condition. Angular rate sensors sense the angular rate of change of movement, such as roll rate, pitch rate, or yaw rate, and produce an output signal indicative of the sensed angular rate of change. A conventional angular rate sensor produces an output voltage signal proportional to the sensed rotational rate of change.
Sensed rate of change events are detected by processing the sensor output voltage signal. These rate events change the sensor output voltage signal much faster than sensor bias drift that is experienced due to temperature changes and aging effects. Many commercially available sensors, such as surface micromachined angular rate sensors, are known to produce an unpredictable non-linear bias drift. As a consequence, the conventional angular rate sensor frequently generates a non-zero, time-varying output signal, even in the absence of a rate of change event. This bias drift may cause an even more significant error in an integration-generated angular position. To minimize this error, the sensor output should be bias drift compensated in order to provide an accurate sensed measurement.
Conventional bias compensation approaches typically employ auxiliary sensors, in lieu of a single angular rate sensor, to compensate for zero-input biases inherent in many angular rate sensors. It should be appreciated that the amount of bias drift may vary depending on the temperature, process imperfections, and stresses due to mechanical shock that the sensor is subjected to and aging.
Accordingly, it is therefore desirable to provide for a method of compensating for bias drift in an output signal of a sensor, such as an angular rate sensor, to produce an output signal having reduced bias drift error. In particular, it is desirable to significantly reduce zero-rate bias drift such that the zero-rate reference is more accurately known and a maximum dynamic range is realized.
In accordance with the teachings of the present invention, a method of removing bias drift from a sensor output is provided. The method includes the steps of sensing a condition with a sensor and generating an output signal, differentiating the output signal, and comparing the differentiated output signal with a threshold difference. The method further includes the steps of determining the presence of bias drift based on the comparison, generating a bias adjustment command signal based on the determined presence of bias drift, and adjusting the output signal generated by the sensor in accordance with the bias adjusted command signal so as to remove bias drift from the output signal. Accordingly, the bias removal method of the present invention compensates for slow varying bias drift for sensors so as to maintain a substantially zero reference and maximize the dynamic range of the sensor.
These and other features, advantages and objects of the present invention will be further understood and appreciated by those skilled in the art by reference to the following specification, claims and appended drawings.